1. Field of the Invention
The present invention relates to an impact transmitting device which is used in impact monitoring operations. More particularly, the present invention relates to an apparatus or detecting and reporting mechanical impacts in reciprocating machines.
2. Description of the Prior Art
The principle of operation of an impact transmitting device for reciprocating machines is to detect free vibrations which are typically symptomatic of machine failure and to transmit the free vibration measurements in the form of an electrical signal. This electrical signal is received by an external logic solver which determines whether or not the reciprocating machine should be powered down. In practice, an impact transmitting device saves unnecessary waste caused by speculative preventative maintenance and increases the life-cycle of reciprocating machine components by alerting operators to early-stage development of harmful mechanical conditions. Such conditions may include loose rod nuts, loose bolts, excessive slipper clearance, worn pins, broken parts, liquid in the process, and rubbing.
In operation, an impact transmitting device is mounted to a reciprocating machine such as a reciprocating compressor having a compressor cylinder assembly. The impact transmitting device detects mechanical impact events in or near the compressor cylinder assembly. The amplitude of each detected impact event is compared to a preset threshold level. If the amplitude of the impact event surpasses the threshold, then the impact event is counted as an “above-threshold impact event.” The number of above-threshold impact events that are counted by the impact transmitting device during a preset time window interval is reported to an external logic solver such as a programmable logic controller (“PLC”) or distributed control system (“DCS”). The external logic solver compares the signal to a predetermined level of acceptable above-threshold impact events during the given time window. If the number of above-threshold level impact events is below the preset acceptable level, then the impact events are disregarded as a “nuisance alarm.” However, if the number is at or above the acceptable level, then the machine is experiencing harmful mechanical events and must be shut down for appropriate maintenance.
While prior art impact transmitting devices offer the ability to detect and report useful mechanical impact data, it has been observed that these devices have at least two deficiencies. First, prior art impact transmitting devices are actually stand-alone rack mounted monitoring systems. As a result, prior art impact transmitting devices are expensive and cumbersome. Second, many prior art impact transmitting devices do not provide for manipulation of the impact threshold level or the time window interval during which the above-threshold impact events are counted. Moreover, the impact transmitter devices that do allow these parameters to be manipulated must be adjusted by using software prior to installation of the device or by an experienced technical person.
In U.S. Pat. No. 6,588,279, an impact transmitting device is disclosed that functions as a single self-contained unit and has an impact transmitting device having a simple “field” adjustable impact threshold level for detecting above-threshold level impact events. The device described in the '279 patent also has a simple field adjustable time window interval during which these above-threshold level impact events are counted.
While the impact transmitting device described in the '279 patent constitutes an advance in the art, it only generates information concerning events which produce a voltage above a preselected threshold voltage. Data respecting lower level impacts in conjunction with data representing higher level impacts is believed by applicant to provide more comprehensive information about the status of a reciprocating machine, and the apparatus in accordance with the present invention provides such data.